Now is as good a time as any. The weaker growing the bush the harder they should be pruned.
Usual advice is to cut back to a few inches of growth and to an outward facing bud.
RHS tried just going over their bushes with a hedge cutter. Gave just as good results as any other type of pruning.

I agree March is as good a time as any. In addition to what Owd has said try to have 2 buds left on each stem just in case hard frost knocks the top one . Or if you are clumsy like me, in case you knock the top bud off.